Spectral and magnetic behavior of some cobalt(II) and nickel(II) complexes involving coordination by the halo group

Abstract

Halo groups attached to benzene rings are capable of occupying coordination positions in some triazene 1-oxide complexes of the general stricture 1. On the basis of comparisons of magnetic moments and electronic spectra of the various complexes with those of one cobalt(II) complex of definitely known structure it is concluded that all the cobalt(II) complexes except one (X = I) are pseudooctahedral both in the solid state and in the solution phase (benzene) in which the complexes are mono-meric. The iodo complex is grossly planar in the crystalline state but becomes pseudooctahedral in the solution phase. All the pseudooctahedral complexes show splitting of the si crystal field band The splittings (which follow the orders F < Cl < Br < I and OCH₃ < SCH₂) are attributed to the low symmetry of the ligand field. In this class of complexes, the octahedral quartet state of cobalt(II) is more readily achieved than the octahedral triplet state d nickel(II). Among nickel-(II) complexes. those having X=OCH₂, OC₂H₂, and SCH₂ show magnetic moments and electronic spectra typical of a dis-toned octahedral geometry both in solid and in solution. On the other hand, nickel(II) complexes with X= halogen are diamagnetic in the crystalline state but become partially paramagnetic In the solution phase. On the basis of spectral and magnetic data it is shown that planar (S=O) preudoonahedral (S=1) equilibria exist in these solutions. The. pseudo- octahedral form invoices halogen coordination. The population of the octahedra/ configuration follows the order F < CI < Br > I. The parameters ΔH°(and ΔS°)for the equilibria are found to be positive. A possible rationalization is discussed on the basis of a simple model.